ESTRO 2022 - Abstract Book

S265

Abstract book

ESTRO 2022

MO-0302 Implementation of high-dose-rate brachytherapy as monotherapy for over-sized prostatic gland

Y. Roussakis 1 , G. Antorkas 1 , A. Antoniou 2 , C. Cloconi 3 , E. Karagiannis 3,4 , K. Ferentinos 3,5 , C. Damianou 2 , I. Strouthos 3,5

1 German Oncology Center, Medical Physics, Limassol, Cyprus; 2 Cyprus University of Technology, Electrical Engineering, Computer Engineering and Informatics, Limassol, Cyprus; 3 German Oncology Center, Radiation Oncology, Limassol, Cyprus; 4 European University Cyprus, Medical School, Limassol, Cyprus; 5 European University Cyprus, Medical School, Nicosia, Cyprus Purpose or Objective Prostatic gland enlargement can be considered a contraindication for high-dose-rate (HDR) brachytherapy (BT). The current study aims to dosimetrically compare prostate HDR BT plans as a function of prostate volume (greater/less than 55 cubic centimetres (cc)), while at the same time evaluating gastrointestinal and genitourinary toxicity through patient reported outcomes (PRO). Materials and Methods Fifty-three patients previously treated for prostate cancer with HDR brachytherapy as monotherapy (2 x 14 Gy) between January 2018 to February 2021 were retrospectively selected. Several dose volume histogram (DVH) statistics for prostate, urethra, rectum, and bladder have been calculated for each plan (two implants per case) and analysed in correlation to prostate volume. Additionally, PRO information was recorded using two validated questionnaires (a. RTOG/EORTC: Radiation Oncology Therapy Group/ European Organization for Research and Treatment of Cancer; b. IPSS: International Prostate System Score), with a baseline before treatment and repeats every 3 months following completion of treatment. Results The median prostate gland volume for the entire cohort (n = 53), <55cc cohort (n = 37), ≥ 55cc cohort (n = 16) was 48.7cc, 34.5cc and 78.8cc, respectively. Median follow up was 9 months. No statistically significant differences (p>0.05) were observed in DVH parameters D 90% , D 100% , V 200% for prostate; D 0.1cc for urethra; and D 0.1cc for rectum. While the dosimetric constraints were met for all plans, significant correlations against prostate volume were observed (p<0.05) in the following DVH parameters were exposed: prostate V 150% ; D 1cc for urethra; D 10% , D 2cc for bladder; and D 1cc , D 2cc , D 10% for rectum. Analysis of PRO measures gathered through the questionnaires to date, does not reveal any significant differences in toxicity between the two groups. Conclusion HDR BT plans created for prostate glands below and above 55cc met all dosimetric objectives and constraints. Significant correlations of certain DVH parameters against prostate volume do not seem to correlate with any clinically measurable toxicity differences between the two cohorts. 1 Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy Purpose or Objective Contouring of organs-at-risk (OARs) and target volumes is an essential step in interventional radiotherapy (brachytherapy, IRT, BT) treatment planning. However, the delineation quality and time spent on contouring depend on the experience of the radiation oncologist. In the last decades, auto-segmentation algorithms have been developed, including atlas-based methods and deep-learning algorithms based. These methods have the potential to reduce inter-and intra-observer variability and speed up the contouring process. This study evaluated existing standard quantitative geometric measures using atlas-based and deep-learning auto-segmentation methods for OARs and target volume in the pelvis. Materials and Methods MIM v. 7.1.5 (MIM Software Inc., Cleveland, OH), installed on a workstation with Intel Xeon 2274 CPU and 16 GB RAM, was used. A total of 23 patients with cervical cancer who underwent Magnetic resonance (MR-based – 1st fraction) and computed tomography (CT-based –1st, 2nd,3rd,4th fractions) interventional radiotherapy (IRT) were included in this study. All the enrolled patients received intracavitary high-dose-rate IRT. Planning CT data were acquired on Optima CT 580 (GE, General Electric) system set on helical scan mode. CT images were reconstructed using a matrix size of 512 × 512 and thickness of 0.625 mm. The planning CT volumes of involved patients for the first and second IRT treatment fraction were collected. Rectum, bladder, small bowel and target volumes (high (HR) and intermediate risk (IR) clinical target volume (CTV) were manually contoured on each CT. An ad hoc workflow was optimized in MIM in order to perform a rigid registration followed by a deformable registration and the subsequent automatic creation of the region of interests (ROIs) on the second CT. The manual ROIs were therefore compared to the automatic ROIs with the use of the Dice Similarity Coefficient (DSC: (2 │ A ∩ B │ / │ A │ + │ B │ ) and the Jaccard Similarity Coefficient (JSC: ( │ A ∩ B │ / │ AUB │ ). It is generally accepted that avalue of DSC and JSC > 0.7 represents excellent agreement. Results Among all structures, the best results were obtained for bladder segmentation with median DSC and JI values of 82% and 70%, respectively. It is mainly because the bladder has a relatively regular shape and clear boundary in the planning CT MO-0303 Evaluation Of Deep-Learning Auto-Segmentation Methods In Cervix Cancer Patients V. Lancellotta 1